Actually, dumpcycle and tapecycle shouldn't be the same.

Rather than adding a few spares, you might want to reduce dumpcycle and
runspercycle, maybe to 2 weeks and 10 tapes. That way, you have a complete
set of backups on the first ten tapes, and another complete set on the next
ten, and AMANDA won't have to play games with the backup set to avoid
overwriting live backups. All your tapes can go in order, because the ten
that MUST be kept are always at least nine tapes away from being needed. 

For maximum protection, your dumpcycle should be as short as possible while
still fitting all your backups and timing requirements. Having more backups
is better. Compare the amount of space you're using on each tape to the
amount available. If you have spare tape, you have room for more backups.

> 
> Amanda is trying to avoid overwriting full backups performed at the
> start of the previous dumpcycle.
> 
> > Does anyone know what I've done wrong?????
> 
> Try increasing the number of tapes that you have available (tapecycle)
> in amanda.conf.  The formula for the tape cycle (from the comments in
> amanda.conf below) is:
> 
> [(dumpcycle in weeks) * (tapes per week)] + [A few more]
>                                             ^^^^^^^^^^^^
> The extra tapes are needed so that amanda does not have to 
> overwrite the
> first full backups of the previous cycle.  I thin the symptoms you're
> seeing suggest that Amanda is trying to avoid this with the tapes that
> it has.
>